The following description relates to emergency power systems and, more specifically, to an emergency power system of an aircraft that includes an energy storage device.
A ram air turbine (RAT) is a wind turbine that is connected to a hydraulic pump and/or electrical generator and is installed in an aircraft. The RAT can be used as a power source and can generate power from the airstream flowing along the aircraft due to the speed of the aircraft.
A key design consideration for each RAT system is low airspeed power production. To further complicate this design consideration, air degradation factors (ADF) that effect airflows must be considered. ADFs may include, but are not limited to, aircraft skin boundary effects, obstructions that obstruct airflows, such as landing gear, buffeting effects, etc. In general, all RAT installations must be designed with consideration for some amount of ADF that makes the available airflow at the RAT disk less than the actual aircraft airspeed.
Early in the design process of an aircraft or a RAT system, ADFs are estimated and the RAT is designed and qualified using this estimation. It is only during flight testing that the accuracy of the estimations can be checked and confirmed. If the estimated ADFs were non-conservative, significant redesign may be required.
In addition to the issues relating to ADFs, it is common for airframe designers to make derivative aircrafts from a certified design while making the new aircraft longer. This can negatively impact the accuracy of the ADF estimations, however, and can result in the RAT being incapable of providing a required level of power at low airspeeds.